JPH0210698A - Device for lighting discharge lamp - Google Patents

Abstract

PURPOSE:To light a discharge lamp by a method wherein a circuit which chopping-controls input to an inverter circuit at the time of startup is provided. CONSTITUTION:With a dc power source 1 turned on, capacitance 20 starts to be charged, a transistor 18 is turned on, an IC 15 for controlling switching is started, and a transistor 3 is switched at specified duty ratio. An inverter circuit 4 is connected to the dc power source 1 when the transistor 3 is on, and intermittently oscillates. At this time, high frequency voltage is intermittently generated from a second coil 8 of an oscillating transformer 8 and applied to a discharge lamp 12 via capacitance 11. A high voltage pulse is generated at the startup of intermittent high frequency voltage, and the discharge lamp 12 starts to light up. On the other hand, the charge level of the capacitance 20 rises to a specified level, the transistor 18 is turned off. After this, the transistor 3 remains on by bias voltage from resistors 13, 14 and the inverter circuit 4 transfers to continuous oscillation. A rated item can be used as the oscillating transformer.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a discharge lamp lighting device using an inverter circuit.

(Prior Art) An inverter circuit is composed of an oscillation transformer, a resonant capacitor, a switching transistor, etc., and is configured to output a high frequency voltage from the secondary side of the oscillation transformer and apply it to the discharge lamp.

Conventionally, when lighting a cold cathode discharge lamp, for example, the rated voltage of the oscillation transformer is adjusted to the voltage during steady lighting of the discharge lamp, and when starting, the oscillation transformer outputs a voltage higher than the rated voltage and discharges the lamp. Devices that start and light electric lights are known.

Note that the time of starting refers to the time from when the power is turned on until the discharge lamp starts lighting.

(Problems to be Solved by the Invention) However, since the oscillation transformer generates a voltage higher than the rated voltage at startup, the transformer is overloaded, causing the transformer to generate considerable heat.

For this reason, it is possible to increase the rating of the oscillation transformer, but if this is done, the transformer becomes large and the problem arises that the circuit cannot be made more compact.

Therefore, the present invention controls the input to the inverter circuit by chopping it at the time of starting, thereby causing the inverter circuit to operate intermittently in oscillation, thereby intermittently generating high-voltage pulses to start and light the discharge lamp. The purpose of the present invention is to provide a discharge lamp lighting device that can be used without any problems due to the heat generated by the transformer.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a discharge lamp lighting device that controls lighting by supplying an oscillation output of an inverter circuit to a discharge lamp, which performs chopping control on input to the inverter circuit at startup. It is equipped with a control circuit.

(Function) In the present invention having such a configuration, the oscillation state of the inverter circuit changes intermittently by chopping the input to the inverter circuit at the time of starting, and an intermittent high-frequency voltage is applied to the discharge lamp. Since high-voltage pulses are generated at each intermittent rise of the high-frequency voltage, high-voltage pulses are intermittently applied to the discharge lamp.

The discharge lamp is started and lit by applying this high voltage pulse.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

1 is a DC power supply, and a push-pull type self-excited inverter circuit 4 is connected to this power supply 1 via a choke coil 2 and an NPN type chopping transistor 3.

The inverter circuit 4 is a well-known circuit composed of a pair of NPN switching transistors 5 and 6, a resonant capacitor 7, an oscillation transformer 8, etc.
, 6 are connected to each end of a primary winding 8a of an oscillation transformer 8, and a resonant capacitor 7 is connected to the primary winding.
are connected in parallel. Further, each of the transistors 5,
The base of 6 is connected to each end of the base winding 8c of the oscillation transformer 8, and is also commonly connected to the center tap of the primary winding 8a of the oscillation transformer 8 via resistors 9 and 10, respectively. A line connected to this intermediate tap constitutes one end of an input terminal and is connected to the choke coil 2. Further, the emitters of the transistors 5 and 6 are connected to each other to form the other end of the input terminal, and the other end is connected to the collector of the chopping transistor 3.

A cold cathode discharge lamp 12 is connected to the output terminal of the inverter circuit 4, that is, to the secondary winding 8b of the oscillation transformer 8 via a capacitor 11.

A voltage dividing circuit formed by connecting resistors 13 and 14 in series is also connected to the DC power supply 1 in parallel, and the connection point of the resistors 13 and 14 is connected to the base of the chopping transistor 3.

In addition, a commercially available switching regulator ICl 3 is connected to the DC power supply 1, and a PNP type transistor 1 is connected to the collector side through a resistor 16, 17 in series.
8 are connected in parallel. and the transistor 18
A resistor 19 is connected between the emitter and the base, and a capacitor 20 is connected between the base and collector via the resistors 16 and 17 in series.

The connection point of the resistors 16 and 17 is connected to one terminal of the switching regulator ICl3. Further, the base of the chopping transistor 3 is connected to another terminal of the switching regulator ICl3.

In this embodiment having such a configuration, when the DC power supply 1 is turned on, charging of the capacitor 20 is started, and a base current flows between the emitter and the base of the transistor 18, and the transistor 18 is turned on.

As a result, a voltage is generated at the connection point between the resistors 16 and 17, and the switching regulator ICl3 comes to operate. Thus, the switching regulator ICl3 causes the chopping transistor 3 to perform a switching operation with a predetermined duty ratio.

When the transistor 3 is turned on, the inverter circuit 4 is connected to the DC power supply 1 via the transistor 3, and therefore performs an oscillation operation during that time. In this way, the inverter circuit 4 operates in oscillation when the chopping transistor 3 is turned on, and therefore operates intermittently in oscillation at the time of starting.

When the inverter circuit 4 intermittently operates in oscillation, a high frequency voltage is intermittently generated from the secondary winding 8b of the oscillation transformer 8 as shown in FIG. 2, and this is applied to the discharge lamp 12 via the capacitor 11. However, at each intermittent rise of the high frequency voltage, a high voltage pulse indicated by a in the figure is generated.

Therefore, at the time of starting, high-voltage pulses are intermittently applied to the discharge lamp 12, so that the discharge lamp 12 is started and lit.

On the other hand, when the charge level of the capacitor 20 reaches a certain level, the base current no longer flows through the transistor 18 and the transistor 18 is turned off.

Thereafter, the chopping transistor 3 is kept in the on state by the bias from the resistors 13 and 14.
The inverter circuit 4 shifts to continuous oscillation operation. In this way, the steady lighting operation of the discharge lamp 12 is maintained.

Figure 3 is a graph showing the relationship between the chopping duty ratio and input voltage at startup when two different discharge lamps are used.This graph shows that if the duty ratio is set to 60%, the input voltage can be minimized. .

In this way, at the time of starting, the input to the inverter circuit 4 is controlled by chopping to intermittent the oscillation operation of the inverter circuit 4, thereby intermittently generating high voltage pulses to start and light the discharge lamp 12. It is sufficient for the transformer 8 to match the rating of the discharge lamp 12 during steady lighting, and therefore there is no need to increase the size of the transformer.

Furthermore, the oscillation transformer will not be overloaded during startup, so there is no risk of abnormal heat generation.

In the above embodiments, a self-excited inverter circuit is used, but the inverter circuit is not necessarily limited to this, and a separately excited inverter circuit may also be used.

Furthermore, although a cold cathode discharge lamp was used as the discharge lamp in the above embodiment, the present invention is not necessarily limited to this, and a hot cathode discharge lamp may be used. In this case, control at the time of starting may be performed by first preheating the engine in the preheating circuit for a certain period of time, and then turning off the preheating circuit to cause the inverter circuit to operate in intermittent oscillation.

[Effects of the Invention] As described in detail above, according to the present invention, the input to the inverter circuit is controlled by chopping at the time of starting, so that the inverter circuit is caused to operate intermittently in oscillation, thereby intermittently generating high voltage pulses. To provide a discharge lamp lighting device that can start and light a discharge lamp, can use a rated oscillation transformer, and does not cause much of a problem with the heat generated by the transformer.

[Brief explanation of the drawing]

The figures show an embodiment of the present invention, and Figure 1 is a circuit diagram;
FIG. 152 is an inverter circuit output waveform diagram at startup, and FIG. 3 is a graph showing the relationship between chopping duty ratio and input voltage at startup for different discharge lamps. 3... Chopping transistor, 4... Inverter circuit, 8... Oscillation transformer, 12... Cold cathode discharge lamp, 15... Switching regulator IC. 18...PNP type transistor, 2o...capacitor.

Claims (2)

[Claims] (1) A discharge lamp lighting device that controls lighting by supplying an oscillation output of an inverter circuit to a discharge lamp, characterized in that the device is provided with a control circuit that performs chopping control on input to the inverter circuit during startup. . (2) The discharge lamp lighting device according to claim (1), wherein the inverter circuit is a self-excited inverter circuit.